spawn: permit using IOBuffer at stdout

People expect to use this (the docs even almost even suggested it at
some point), so it is better to make it work as expected (and better
than they can emulate) than to criticize their choices.

Also fix a few regressions and handling mistakes in setup_stdios:
 - #44500 tried to store a Redirectable into a SpawnIO, dropping FileRedirect
 - CmdRedirect did not allocate a ProcessChain, so it wouldd call
   setup_stdio then call setup_stdios on the result of that, which is
   strongly discouraged as setup_stdio(s) should only be called once
 - BufferStream was missing `check_open` calls before writing, and
   ignored `Base.reseteof` as a possible means of resuming writing after
   `closewrite` sends a shutdown message. Currently this fix is disabled
   because Pkg seems like a bit of a disaster with IO mismanagement.
 - Add `closewrite` to more methods, and document it.

Fixes #39311
Fixes #49234
Closes #49233
Closes #46768

NEWS.md

@@ -72,6 +72,14 @@ New library features
   write the output to a stream rather than returning a string ([#48625]).
 * `sizehint!(s, n)` now supports an optional `shrink` argument to disable shrinking ([#51929]).
 * New function `Docs.hasdoc(module, symbol)` tells whether a name has a docstring ([#52139]).
+* Passing an IOBuffer as a stdout argument for Process spawn now works as
+  expected, synchronized with `wait` or `success`, so a `Base.BufferStream` is
+  no longer required there for correctness to avoid data-races ([#TBD]).
+* After a process exits, `closewrite` will no longer be automatically called on
+  the stream passed to it. Call `wait` on the process instead to ensure the
+  content is fully written, then call `closewrite` manually to avoid
+  data-races. Or use the callback form of `open` to have all that handled
+  automatically.
 
 Standard library changes
 ------------------------

base/coreio.jl

@@ -11,6 +11,7 @@ struct DevNull <: IO end
 const devnull = DevNull()
 write(::DevNull, ::UInt8) = 1
 unsafe_write(::DevNull, ::Ptr{UInt8}, n::UInt)::Int = n
+closewrite(::DevNull) = nothing
 close(::DevNull) = nothing
 wait_close(::DevNull) = wait()
 bytesavailable(io::DevNull) = 0

base/exports.jl

@@ -1155,6 +1155,16 @@ public
     @locals,
     @propagate_inbounds,
 
+# IO
+    # types
+    BufferStream,
+    IOServer,
+    OS_HANDLE,
+    PipeEndpoint,
+    TTY,
+    # functions
+    reseteof,
+
 # misc
     notnothing,
     runtests,

base/filesystem.jl

@@ -143,6 +143,8 @@ function close(f::File)
     nothing
 end
 
+closewrite(f::File) = nothing
+
 # sendfile is the most efficient way to copy from a file descriptor
 function sendfile(dst::File, src::File, src_offset::Int64, bytes::Int)
     check_open(dst)

base/io.jl

@@ -25,6 +25,14 @@ end
 
 lock(::IO) = nothing
 unlock(::IO) = nothing
+
+"""
+    reseteof(io)
+
+Clear the EOF flag from IO so that further reads (and possibly writes) are
+again allowed. Note that it may immediately get re-set, if the underlying
+stream object is at EOF and cannot be resumed.
+"""
 reseteof(x::IO) = nothing
 
 const SZ_UNBUFFERED_IO = 65536
@@ -68,6 +76,10 @@ Shutdown the write half of a full-duplex I/O stream. Performs a [`flush`](@ref)
 first. Notify the other end that no more data will be written to the underlying
 file. This is not supported by all IO types.
 
+If implemented, `closewrite` causes subsequent `read` or `eof` calls that would
+block to instead throw EOF or return true, respectively. If the stream is
+already closed, this is idempotent.
+
 # Examples
 ```jldoctest
 julia> io = Base.BufferStream(); # this never blocks, so we can read and write on the same Task

base/iobuffer.jl

@@ -349,7 +349,6 @@ eof(io::GenericIOBuffer) = (io.ptr-1 == io.size)
 
 function closewrite(io::GenericIOBuffer)
     io.writable = false
-    # OR throw(_UVError("closewrite", UV_ENOTSOCK))
     nothing
 end
 

base/iostream.jl

@@ -63,6 +63,8 @@ function close(s::IOStream)
     systemerror("close", bad)
 end
 
+closewrite(s::IOStream) = nothing
+
 function flush(s::IOStream)
     sigatomic_begin()
     bad = @_lock_ios s ccall(:ios_flush, Cint, (Ptr{Cvoid},), s.ios) != 0

base/process.jl

@@ -6,11 +6,12 @@ mutable struct Process <: AbstractPipe
     in::IO
     out::IO
     err::IO
+    syncd::Vector{Task}
     exitcode::Int64
     termsignal::Int32
     exitnotify::ThreadSynchronizer
-    function Process(cmd::Cmd, handle::Ptr{Cvoid})
-        this = new(cmd, handle, devnull, devnull, devnull,
+    function Process(cmd::Cmd, handle::Ptr{Cvoid}, syncd::Vector{Task})
+        this = new(cmd, handle, devnull, devnull, devnull, syncd,
                    typemin(fieldtype(Process, :exitcode)),
                    typemin(fieldtype(Process, :termsignal)),
                    ThreadSynchronizer())
@@ -35,6 +36,15 @@ end
 pipe_reader(p::ProcessChain) = p.out
 pipe_writer(p::ProcessChain) = p.in
 
+# a lightweight pair of a child OS_HANDLE and associated Task that will
+# complete only after all content has been read from it for synchronizing
+# state without the kernel to aide
+struct SyncCloseFD
+    fd
+    t::Task
+end
+rawhandle(io::SyncCloseFD) = rawhandle(io.fd)
+
 # release ownership of the libuv handle
 function uvfinalize(proc::Process)
     if proc.handle != C_NULL
@@ -74,8 +84,8 @@ function _uv_hook_close(proc::Process)
     nothing
 end
 
-const SpawnIO  = Union{IO, RawFD, OS_HANDLE}
-const SpawnIOs = Vector{SpawnIO} # convenience name for readability
+const SpawnIO  = Union{IO, RawFD, OS_HANDLE, SyncCloseFD} # internal copy of Redirectable, removing FileRedirect and adding SyncCloseFD
+const SpawnIOs = Memory{SpawnIO} # convenience name for readability (used for dispatch also to clearly distinguish from Vector{Redirectable})
 
 function as_cpumask(cpus::Vector{UInt16})
     n = max(Int(maximum(cpus)), Int(ccall(:uv_cpumask_size, Cint, ())))
@@ -100,6 +110,7 @@ end
                 error("invalid spawn handle $h from $io")
             end
             for io in stdio]
+        syncd = Task[io.t for io in stdio if io isa SyncCloseFD]
         handle = Libc.malloc(_sizeof_uv_process)
         disassociate_julia_struct(handle)
         (; exec, flags, env, dir) = cmd
@@ -117,7 +128,7 @@ end
             cpumask === nothing ? 0 : length(cpumask),
             @cfunction(uv_return_spawn, Cvoid, (Ptr{Cvoid}, Int64, Int32)))
         if err == 0
-            pp = Process(cmd, handle)
+            pp = Process(cmd, handle, syncd)
             associate_julia_struct(handle, pp)
         else
             ccall(:jl_forceclose_uv, Cvoid, (Ptr{Cvoid},), handle) # will call free on handle eventually
@@ -130,23 +141,24 @@ end
     return pp
 end
 
-_spawn(cmds::AbstractCmd) = _spawn(cmds, SpawnIO[])
+_spawn(cmds::AbstractCmd) = _spawn(cmds, SpawnIOs())
 
-# optimization: we can spawn `Cmd` directly without allocating the ProcessChain
-function _spawn(cmd::Cmd, stdios::SpawnIOs)
-    isempty(cmd.exec) && throw(ArgumentError("cannot spawn empty command"))
+function _spawn(cmd::AbstractCmd, stdios::Vector{Redirectable})
     pp = setup_stdios(stdios) do stdios
-        return _spawn_primitive(cmd.exec[1], cmd, stdios)
+        return _spawn(cmd, stdios)
     end
     return pp
 end
 
+# optimization: we can spawn `Cmd` directly without allocating the ProcessChain
+function _spawn(cmd::Cmd, stdios::SpawnIOs)
+    isempty(cmd.exec) && throw(ArgumentError("cannot spawn empty command"))
+    return _spawn_primitive(cmd.exec[1], cmd, stdios)
+end
+
 # assume that having a ProcessChain means that the stdio are setup
 function _spawn(cmds::AbstractCmd, stdios::SpawnIOs)
-    pp = setup_stdios(stdios) do stdios
-        return _spawn(cmds, stdios, ProcessChain())
-    end
-    return pp
+    return _spawn(cmds, stdios, ProcessChain())
 end
 
 # helper function for making a copy of a SpawnIOs, with replacement
@@ -212,7 +224,7 @@ end
 
 
 # open the child end of each element of `stdios`, and initialize the parent end
-function setup_stdios(f, stdios::SpawnIOs)
+function setup_stdios(f, stdios::Vector{Redirectable})
     nstdio = length(stdios)
     open_io = SpawnIOs(undef, nstdio)
     close_io = falses(nstdio)
@@ -295,25 +307,26 @@ function setup_stdio(stdio::IO, child_readable::Bool)
     child = child_readable ? rd : wr
     try
         let in = (child_readable ? parent : stdio),
-            out = (child_readable ? stdio : parent)
-            @async try
+            out = (child_readable ? stdio : parent),
+            t = @async try
                 write(in, out)
             catch ex
                 @warn "Process I/O error" exception=(ex, catch_backtrace())
+                rethrow()
             finally
                 close(parent)
-                child_readable || closewrite(stdio)
             end
+            return (SyncCloseFD(child, t), true)
         end
     catch
         close_pipe_sync(child)
         rethrow()
     end
-    return (child, true)
 end
 
-close_stdio(stdio::OS_HANDLE) = close_pipe_sync(stdio)
 close_stdio(stdio) = close(stdio)
+close_stdio(stdio::OS_HANDLE) = close_pipe_sync(stdio)
+close_stdio(stdio::SyncCloseFD) = close_stdio(stdio.fd)
 
 # INTERNAL
 # pad out stdio to have at least three elements,
@@ -325,19 +338,19 @@ close_stdio(stdio) = close(stdio)
 #   - An Filesystem.File or IOStream object to redirect the output to
 #   - A FileRedirect, containing a string specifying a filename to be opened for the child
 
-spawn_opts_swallow(stdios::StdIOSet) = SpawnIO[stdios...]
-spawn_opts_inherit(stdios::StdIOSet) = SpawnIO[stdios...]
+spawn_opts_swallow(stdios::StdIOSet) = Redirectable[stdios...]
+spawn_opts_inherit(stdios::StdIOSet) = Redirectable[stdios...]
 spawn_opts_swallow(in::Redirectable=devnull, out::Redirectable=devnull, err::Redirectable=devnull) =
-    SpawnIO[in, out, err]
+    Redirectable[in, out, err]
 # pass original descriptors to child processes by default, because we might
 # have already exhausted and closed the libuv object for our standard streams.
 # ref issue #8529
 spawn_opts_inherit(in::Redirectable=RawFD(0), out::Redirectable=RawFD(1), err::Redirectable=RawFD(2)) =
-    SpawnIO[in, out, err]
+    Redirectable[in, out, err]
 
 function eachline(cmd::AbstractCmd; keep::Bool=false)
     out = PipeEndpoint()
-    processes = _spawn(cmd, SpawnIO[devnull, out, stderr])
+    processes = _spawn(cmd, Redirectable[devnull, out, stderr])
     # if the user consumes all the data, also check process exit status for success
     ondone = () -> (success(processes) || pipeline_error(processes); nothing)
     return EachLine(out, keep=keep, ondone=ondone)::EachLine
@@ -385,20 +398,20 @@ function open(cmds::AbstractCmd, stdio::Redirectable=devnull; write::Bool=false,
         stdio === devnull || throw(ArgumentError("no stream can be specified for `stdio` in read-write mode"))
         in = PipeEndpoint()
         out = PipeEndpoint()
-        processes = _spawn(cmds, SpawnIO[in, out, stderr])
+        processes = _spawn(cmds, Redirectable[in, out, stderr])
         processes.in = in
         processes.out = out
     elseif read
         out = PipeEndpoint()
-        processes = _spawn(cmds, SpawnIO[stdio, out, stderr])
+        processes = _spawn(cmds, Redirectable[stdio, out, stderr])
         processes.out = out
     elseif write
         in = PipeEndpoint()
-        processes = _spawn(cmds, SpawnIO[in, stdio, stderr])
+        processes = _spawn(cmds, Redirectable[in, stdio, stderr])
         processes.in = in
     else
         stdio === devnull || throw(ArgumentError("no stream can be specified for `stdio` in no-access mode"))
-        processes = _spawn(cmds, SpawnIO[devnull, devnull, stderr])
+        processes = _spawn(cmds, Redirectable[devnull, devnull, stderr])
     end
     return processes
 end
@@ -415,12 +428,18 @@ function open(f::Function, cmds::AbstractCmd, args...; kwargs...)
     P = open(cmds, args...; kwargs...)
     function waitkill(P::Union{Process,ProcessChain})
         close(P)
-        # 0.1 seconds after we hope it dies (from closing stdio),
-        # we kill the process with SIGTERM (15)
-        local t = Timer(0.1) do t
+        # shortly after we hope it starts cleanup and dies (from closing
+        # stdio), we kill the process with SIGTERM (15) so that we can proceed
+        # with throwing the error and hope it will exit soon from that
+        local t = Timer(2) do t
             process_running(P) && kill(P)
         end
-        wait(P)
+        # pass false to indicate that we do not care about data-races on the
+        # Julia stdio objects after this point, since we already know this is
+        # an error path and the state of them is fairly unpredictable anyways
+        # in that case. Since we closed P some of those should come crumbling
+        # down already, and we don't want to throw that error here either.
+        wait(P, false)
         close(t)
     end
     ret = try
@@ -430,10 +449,23 @@ function open(f::Function, cmds::AbstractCmd, args...; kwargs...)
         rethrow()
     end
     close(P.in)
+    closestdio = @async begin
+        # wait for P to complete (including sync'd), then mark the output streams for EOF (if applicable to that stream type)
+        wait(P)
+        err = P.err
+        applicable(closewrite, err) && closewrite(err)
+        out = P.out
+        applicable(closewrite, out) && closewrite(out)
+        nothing
+    end
+    # now verify that the output stream is at EOF, and the user didn't fail to consume it successfully
+    # (we do not currently verify the user dealt with the stderr stream)
     if !(eof(P.out)::Bool)
         waitkill(P)
         throw(_UVError("open(do)", UV_EPIPE))
     end
+    # make sure to closestdio is completely done to avoid data-races later
+    wait(closestdio)
     success(P) || pipeline_error(P)
     return ret
 end
@@ -650,26 +682,31 @@ function process_status(s::Process)
            error("process status error")
 end
 
-function wait(x::Process)
-    process_exited(x) && return
-    iolock_begin()
+function wait(x::Process, syncd::Bool=true)
     if !process_exited(x)
-        preserve_handle(x)
-        lock(x.exitnotify)
-        iolock_end()
-        try
-            wait(x.exitnotify)
-        finally
-            unlock(x.exitnotify)
-            unpreserve_handle(x)
+        iolock_begin()
+        if !process_exited(x)
+            preserve_handle(x)
+            lock(x.exitnotify)
+            iolock_end()
+            try
+                wait(x.exitnotify)
+            finally
+                unlock(x.exitnotify)
+                unpreserve_handle(x)
+            end
+        else
+            iolock_end()
         end
-    else
-        iolock_end()
+    end
+    # and make sure all sync'd Tasks are complete too
+    syncd && for t in x.syncd
+        wait(t)
     end
     nothing
 end
 
-wait(x::ProcessChain) = foreach(wait, x.processes)
+wait(x::ProcessChain, syncd::Bool=true) = foreach(p -> wait(p, syncd), x.processes)
 
 show(io::IO, p::Process) = print(io, "Process(", p.cmd, ", ", process_status(p), ")")